Well first of all, games only start making use of all those cores so you'd be better off with a high speed dual core right now. The "Pro" in the name also kinda clashes with "gamer". ?
If you're a gamer get a Dell (they got some nice stuff for great prices) or build your own. Games don't really run on OSX so you'd have to install some esoteric Windows that will run poorly on those machines. If you want to use your Mac for gaming, get a Macbook pro or iMac. The Mac Pro just isn't for you, you can get a Dell gaming PC, then another better one in 18 months for the same price.